A display apparatus having a display panel with liquid crystal or the like uses a backlight device employing an LED (Light Emitting Diode) or the like as a light source, to display a character, an image, a video image and the like on a screen by making light enter from the back surface side of the display panel. For example, a small- or medium-sized backlight device for liquid-crystal display used in a mobile phone, mobile terminal or the like often employs an edge light type in which light enters an end face of a light guide plate to be outputted from a plate surface of the light guide plate, in order to realize thinning of the device.
Japanese Patent Application Laid-Open Publication No. 2009-199871 discloses a display apparatus using a backlight device of an edge light type. The display apparatus includes a display element (corresponding to a display panel) on which a picture of a guide lamp is printed, a light guide plate which irradiates a rear surface of the display element with light, a light source which emits light entering the light guide plate, and a light source holder which holds the light source. The light guide plate has a thin rectangular shape, and a light entering surface is formed on a side surface substantially orthogonal to a main surface thereof. The light guide plate has a light guiding part having a tapered shape which has an increased thickness on the side of the light entering surface within a predetermined area of the light entering surface side.
A plurality of LEDs of a top view type are used as the light source, the LEDs being arranged on a surface of a strip-shaped LED mounting substrate, while the LED mounting substrate being opposed to the light entering surface of the light guide plate. The light source holder has an L shape, and has a bottom part located along the light guide plate as well as a side part substantially orthogonal to the bottom part and to which the LED mounting substrate is attached. The LEDs of the top view type arranged on the surface of the LED mounting substrate emits light with the surface normal direction of the LED mounting substrate determined as a main direction, and the light enters into the light guiding part from the light entering surface of the light guide plate. Since the light guiding part has a tapered shape in which the thickness thereof decreases from the light entering surface side toward the middle part of the light guide plate, the light entering from the light entering surface is reflected by the inclined surface of the tapered shape while being guided to the middle part of the light guide plate, and is outputted from the main surface of the light guide plate. In the display apparatus according to Japanese Patent Application Laid-Open Publication No. 2009-199871, therefore, since the light guide plate has the tapered light guiding part which allows a larger amount of light to enter from the light entering surface, it is possible to attempt thinning of the light guide plate and also of the display apparatus.
In general, the light guide plate as disclosed in Japanese Patent Application Laid-Open Publication No. 2009-199871 is fabricated by injection molding. Though it has been required for a middle-or small-sized light guide plate used for a mobile phone or mobile terminal to be thinner, in injection molding, there are constraints of the panel size for thinning of the light guide plate. In the current circumstances, the thickness of approximately 1.0 mm is the main stream for a light guide plate having the size of approximately several to ten inches, and practical realization has been expected for an even thinner light guide plate having the thickness of approximately 0.3 mm.